Add CI fixes and improvements (#780)

* Update GolangCI-lint and lint config

The `algo` parameter for the `unparam` linter has been removed and we
should thus no longer specify it. Also, bumping the GolangCI-lint
version to the latest available minor release.

See: mvdan/unparam@e6a6d1c51b

* Fix and improve bintray CI script

* Further CI setup improvements

* Split-out CI steps into stand-alone scripts

ci/bintray.sh

@@ -1,5 +1,8 @@
-#!/bin/bash
-go version | grep go1.11 || exit
+#!/usr/bin/env bash
+set -u -e -x -o pipefail
+
+go version | grep go1.12 || exit
+
 VERSION=$(git describe --tags)
 mkdir ci/binaries
 GOOS=windows GOARCH=amd64 go build -ldflags "-s -w -X main.githash=$(git log --pretty=format:'%h' -n 1)" -o ci/binaries/matterbridge-$VERSION-windows-amd64.exe